Optical recording medium

Abstract

An optical recording medium is disclosed which comprises a reflecting material, the surface of which is characterized by cavities of average depth D and of average spacing S such that for incident radiation of wavelength λ, S is less than about λ/20 and D is either greater than λ/6 or less than λ/6 and is capable of being altered to either less than or greater than λ/6, respectively. In the practice of the invention, the heat from a high intensity energy source, such as a laser operating in the ultraviolet, optical or near-infrared region or a beam of electrons, softens the reflective material at the surface and, depending on the sign of the surface energy, either increases or decreases D, thus lowering or raising the reflectivity of the surface, respectively.

What is claimed is: 
     
       1. An optical recording medium comprising a surface which is characterized as having cavities of average depth D and average spacing S such that for contemplated incident radiation of wavelength λ, S is less than about λ/20 and D is either greater than or less than about λ/6 and is capable of being selectively altered to either less than or greater than about λ/6, respectively, said altered surface having respectively decreased or increased reflectivity of said incident radiation therefrom. 
     
     
       2. The optical recording medium of claim 1 in which D is greater than about λ/6. 
     
     
       3. The optical recording medium of claim 1 in which D is less than about λ/6. 
     
     
       4. The optical recording medium of claim 1 in which λ ranges from about 0.1 to 2.0 μm. 
     
     
       5. The optical recording medium of claim 1 in which a substrate supports the reflecting material. 
     
     
       6. The optical recording medium of claim 1 in which an optically transparent layer, capable of substantial transparency to incident radiation, coats the surface of the reflecting material. 
     
     
       7. A process for recording information on an optical recording medium by exposing selected portions of the optical recording medium to an optical signal having a wavelength the optical recording medium comprising a surface characterized by cavities of average depth D and average spacing S such that for incident radiation of wavelength λ, S is less than about λ/20 and D is either greater than or less than about λ/6 prior to irradiation and either less than or greater than about λ/6, respectively, following irradiation wherein altering the average depth D to less than or greater than about λ/6 respectively increases or decreases the reflectively of the exposed selected portions of the optical recording medium. 
     
     
       8. The process of claim 7 in which the reflecting material is formed on a supporting substrate. 
     
     
       9. The process of claim 7 in which an optically transparent layer coats the surface of the high reflectivity material. 
     
     
       10. The process of claim 7 in which the optical signal comprises coherent electromagnetic radiation. 
     
     
       11. The process of claim 7 in which the optical signal has a wavelength λ ranging from about 0.1 to 2.0 μm. 
     
     
       12. The process of claim 7 in which following exposure D is greater than 6/λ and the reflectivity of the surface in the exposed selected portions of said optical recording medium is reduced. 
     
     
       13. The process of claim 7 in which following exposure D is less than 6/λ and the reflectivity of the surface in the exposed selected portions of said optical recording medium is increased. 
     
     
       14. A process for fabricating an optical recording medium which comprises forming a graded, textured surface on a reflecting material characterized by cavities of average depth D and of average spacing S such that for contemplated incident radiation of wavelength λ, S is less than about λ/20 and D is either greater than or less than about λ/6 and is capable of being altered to either less than or greater than about λ/6, respectively. 
     
     
       15. The process of claim 14 in which the reflecting material is formed on a supporting substrate. 
     
     
       16. The process of claim 14 in which an optically transparent layer coats the surface of the high reflectivity material. 
     
     
       17. The process of claim 14 in which the cavities are formed by particle track etching which process comprises (a) bombarding a dielectric material with high energy particles, thereby generating damage tracks, and (b) etching said damage tracks to form cavities of average depth D and average spacing S. 
     
     
       18. The process of claim 14 in which the ratio of depth to spacing of the cavities is at least about 5. 
     
     
       19. The process of claim 14 in which the surface is bombarded with high energy particles having a particle density ranging from about 1×10 10  to 4×10 12  cm -2 .